Error if union type has same property with different nullability in two types

[yonigibbs]

Hi! I seem to be hitting an issue where I have a union type, and two of the types in that union share a common field, with different nullability. For example:

type Size {
    height: Int!
    weight: Int!
}

type Cat {
    name: String!
    size: Size!         # `size` is REQUIRED on `Cat`
}

type Mouse {
    name: String!
    size: Size         # `size` is OPTIONAL on `Mouse`
}

When I query for this, the error I get is:

java.lang.IllegalStateException: Validation error of type FieldsConflict: size: fields have different nullability shapes @ 'animals'

Is there something I should be configuring to get around this? Or is this a bug?

There is a repo where this can be reproduced here: https://github.com/yonigibbs/graphql-union-type

Thanks!

[oliemansm]

This isn't a problem of this library. Instead it appears to be an intended check by graphql-java: https://github.com/graphql-java/graphql-java/blob/2e1e9897030f61a6e9a2c2eba358fd87da1d20d0/src/main/java/graphql/validation/rules/OverlappingFieldsCanBeMerged.java#L178.

Haven't checked the GraphQL specification, but if according the specification this should be allowed you could raise an issue in the graphql-java project.

[yonigibbs]

Thanks @oliemansm. Did a bit more digging to see if this is allowed in the schema and found this very similar issue: graphql/graphql-js#1361. There's some discussion there, and a workaround in the first response.